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OBS Motor Compatibility

Discussion in 'Chevy Trucks' started by mayhem, Sep 4, 2009.

  1. mayhem

    mayhem PlowSite.com Addict
    from Peru MA
    Messages: 1,016

    My sister has a 96 or 97 (not positive, but I think its a 96) 3/4 ton (a real 3/4 ton...8600gvwr, 8 bolt wheels, boxed frame rails, etc) GMC Sierra with a blown motor. Can any 350 out of an OBS work without major electrical modifications? She's looking at a pretty expensive repair job that she simply cannot afford so I'm trying to help her find a decent core out of a wrecked truck that she can have installed and save a few bucks. I have a local ad for a "good running 350 out of a 93 Chevy 4x4" for $350. Decent price, I don't have any details and have not called on it. The first question I have though is, will it work in her truck without major modifications? I don't want to have to change the computer and the wiring harnesses and all that...looking for the best way to advise her to proceed so she doesn't get totally screwed over.
     
  2. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    If you want a direct swap you need a '96-2000 (OBS) Vortec engine. Nothing else will be a "direct install" due to the Vortec injection with it's unique intake bolt pattern.
     
  3. Sydenstricker Landscaping

    Sydenstricker Landscaping PlowSite Veteran
    Messages: 3,882

    Is the bottom end just junk, or is the whole thing?? Correct me if I am wrong, but you shold be able to bolt the Vortec top end to an older 350 block. So as long as the top end is in good shape (heads, intake, cam, etc) are good, then you should be able to make it work. But I could be wrong and you would need a 96-98 engine. I think the 98-99 obs trucks were starting to go with the LS1 version of the 5.7.
     
  4. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    '96-'00 Vortec heads and injection will go right onto the pre-'96 engines but you lose the CKP (crankshaft position sensor) capability to run the injection as there's no reluctor ring on the pre '96 cranks for the CKP to read. However there is a company that makes an add on reluctor that goes right onto the earlier crankshaft to make the swap possible. You also have to use the '96-'00 Vortec timing cover so you have a means to mount the CKP.

    No LS1 based engine's in the OBS trucks Tom. Trucks didn't get them until the Silverado body was released in '99 but none were 5.7L. It was either 4.8, 5.3 or 6.0. Not to say that they aren't an excellent match though. :D

    To the OP, like I mentioned a '96-'00 OBS Vortec is what you want if you require a direct fit.
     
  5. mayhem

    mayhem PlowSite.com Addict
    from Peru MA
    Messages: 1,016

    Found out its a 97, still the same answer applies, thanks B&B.

    Not sure what the actual problem is with the OEM motor, but she said "blown". Not totally descriptive, but its all I've got.
     
  6. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    I'd want to know exactly what "blown" meant before I went much further as the CPI Vortec engines are pretty tough and don;t just blow up for no reason. Unless it's been run with coolant in the oil from a leaky intake gasket or it blew and oil cooler line, which they're well known for. Then it's likely done for.
     
  7. second b&bs opinion(which from my reading is pretty informed). my 96 started running like a rock one morning a badly tuned rock. Just like you threw a switch from good to rock. good fuel pressure, spark, compression, no codes, was the pos factory fuel injection set up, the "spider" assy. replaced with the updated one with outboard injectors(availiable from gm) and presto!! you would have sworn it had a dead cylinder or two. may want to have someone knowledgable check it out first you never know... I have fixed "blown\seized" up motors by changing\replacing altenators, injectors, transmission bell bolts, lifters, motor mounts,(it clunks\rattles real bad under load, I guess so!!) mine is still running strong. Lots of those trucks had intake gaskets done early in life if your looking at donor motors in the wrecking yard check the air conditioning compressor mount under the compressor to se
    e if it has been notched out to allow removal of the intake bolt underneath it. lots of shops did this because it is faster and you wouldn't see it unless you looked pretty hard. Its a pretty surefire indicator there is a new gasket under there. If it is a reasonably low mile motor and the intake gasket has been done you should get a lot of life out of it.